Video production: FreeLens, English subtitles available
What is the challenge about?
The task is clear:
The person or team with the most clean layers in their cocktail after 10 minutes wins.
It's not just about skill, but also logical thinking. The students have to figure out the order in which the colored sugar solutions can be layered on top of each other based on their different densities. To do this, they have to carefully examine the layers in the 5 test tubes they are shown.
Key data:
- Topic: Density, pipetting, logic puzzles
- Duration: 20-30 minutes
- Teams: Individually or in teams of two
Photo 1: 5 test tubes that are shown to the students and that they must use to figure out the correct layering order.
Photo 2: Solution
Rules:
Only clearly separated colors count.
Mixed colors (e.g., brown) do not count.
Each color may only be used once.
Anyone who has correctly layered all colors wins immediately.
Materials & Preparation
Materials per team:
- 2 test tubes
- 6 pipettes (one per sugar solution)
- 1 test tube rack
- 6 sugar solutions of different concentrations (can be shared among several teams)
- 1 spray bottle with water (can also be shared)
- Paper towels
- 1 waste container for used solutions
- 5 test tubes, each containing 3 colors layered on top of each other (important: use the same combinations as in the video). These combinations can also be projected as a photo onto a screen — the main thing is that all teams can see them.
Materials for preparing the sugar solutions (for the teacher):
- Kettle
- 1 kg sugar
- 500 ml water
- Measuring cup
- Yellow, red, and blue food coloring
- 6 small containers (e.g., beakers)
Tips for preparing the sugar solutions
Step 1: Make a maximum-density solution
Dissolve 1 kg of sugar in 500 ml of warm water. Double the amount if needed.
Step 2: Gradually dilute the solution
Divide the volume into several containers (e.g., 6 beakers):
- Beaker 1: only water
- Beaker 2: 1/5 sugar solution, fill the rest with water
- Beaker 3: 2/5 sugar solution, fill the rest with water
- Beaker 4: 3/5 sugar solution, fill the rest with water
- Beaker 5: 4/5 sugar solution, fill the rest with water
- Beaker 6: only sugar solution (the densest solution)
Step 3: Color strongly
Do not be sparing with the coloring — only strongly colored solutions create clear layers (about 10 drops per solution).
As a reminder:
Green is made by mixing blue and yellow.
Purple comes from red and blue.
Orange comes from yellow and red.
Step 4: Test / create reference combinations
Check the layering order by preparing both the full density cocktail and the 5 test tubes that students will use to determine the correct color sequence.
You only need to prepare the color combinations once — display them clearly, project a photo, or distribute them to the class.
Is the challenge too difficult or too easy for your students?
This challenge can easily be adapted to the level of your students. It can therefore be carried out both in primary school and in secondary school (lycée).
Here is how you can make the challenge easier or more difficult:
Easier – (suitable for primary school age)
Show the students as many color combinations as possible, with only two solutions layered on top of each other in each test tube.
More difficult – Challenge like in the show
In this version, no ready-made solutions are provided:
The teams have to mix the sugar solutions themselves — without a recipe. They only have sugar, water, and food coloring available.
This version takes longer (in the show, more than one hour) and can also get a bit messier 😉
And once everything is finished, the students can even taste their density cocktail — very sweet, but educational 😉
Have fun experimenting!
Challenge idea: Michèle Weber (FNR)
Author: Lucie Zeches (FNR)
Editor: Joseph Rodesch (FNR)
Die Ausarbeitung dieser Rubrik wurde von science.lu in Kooperation mit dem Script (Service de Coordination de la Recherche et de l´Innovation pédagogiques et technologiques) durchgeführt.
